S-8351A20MC-J2FT2X Datasheet, PDF (23/51 Pages) Seiko Instruments Inc – SWITCHING REGULATOR CONTROLLER

STEP-UP, BUILT-IN / EXTERNAL FET PFM CONTROL SWITCHING REGULATOR / SWITCHING REGULATOR CONTROLLER
Rev.3.0_01
S-8351/8352 Series
5. VDD / VOUT Separate Type (For S-8351/8352 Series D Type)
The D type provides separate internal circuit power supply (VDD pin) and output voltage setting pin (VOUT pin) in the
IC, making it ideal for the following applications.
(1) Changing the output voltage value using an external resistor
(2) Setting a high output voltage value, such as +15 V
Cautions 1. This IC starts a step-up operation at VDD = 0.8 V, but set 1.8 ≤ VDD ≤ 10 V to stabilize the output
voltage and frequency of the oscillator. (Input a voltage of 1.8 V or more at the VDD pin for all
products with a setting less than 1.9 V.) An input voltage of 1.8 V or more at the VDD pin allows
connection of the VDD pin to either the input voltage VIN pin or output VOUT pin.
2. Choose external resistors RA and RB so as to not affect the output voltage, considering that there
is impedance between the VOUT pin and VSS pin in the IC chip. The internal resistance
between the VOUT pin and VSS pin is as follows :
(1) S-835xx18 : 2.1 MΩ to 14.8 MΩ
(2) S-835xx20 : 1.4 MΩ to 14.8 MΩ
(3) S-835xx30 : 1.4 MΩ to 14.2 MΩ
(4) S-835xx50 : 1.4 MΩ to 12.1 MΩ
3. Attach a capacitor (CC) in parallel to the RA resistance when an unstable event such as
oscillation of the output voltage occurs. Calculate CC using the following equation :
C_C
[
F
]=
2
•
π
1
•R_A •
20
kHz
23